Flow control valves are typically used to regulate the flow or pressure of a fluid in a device. Flow control valves may be found in various applications such as commercial vehicles and aerospace applications. These types of control valves may respond to signals generated by independent devices that measure the flow and temperature across the valve. Prior art flow control valves generally include a diaphragm having a differential pressure across the diaphragm, wherein movement of the diaphragm controls the flow through the valve member. More specifically, the diaphragm changes shape with inlet pressure changes, thus maintaining a constant flow rate through the valve. Although, these current flow control valves are an improvement over earlier devices due to their simple structure, they may not prevent an undesired change to the flow rate setpoint of the valve when exposed to high temperatures.
A typical flow control valve assembly may include at least a housing, a diaphragm, and a diaphragm support structure. As previously stated, these devices may be short lived when exposed to high temperatures and pressures. Accordingly, the flow control valve assembly may include a sensing device, such as a zero delta-pressure servo sensor, to maintain an approximately zero pounds per square inch differential (psid) across the diaphragm for optimal operation. The zero psid is initially calibrated at room temperature. This initial calibration is such that the diaphragm is stroked to a position away from its natural center. The diaphragm stroke required to calibrate the valve is typically less than 0.100 inches and is thus considered a small stroke application. As the valve body temperature increases, the diaphragm introduces an additional force which upsets the zero delta-pressure balance originally established at room temperature.
In many instances, the diaphragm may be made from a flat sheet of fabric having a number of yarns, and may be coated on at least one side with an elastomer, which is subsequently crosslinked. The diaphragm support structure typically includes two metallic housings that serve to fixedly hold the diaphragm therebetween via a plurality of torqued bolts formed in a pattern about an outer diameter. During the operation of the valve, the diaphragm may be exposed to numerous pressure cycles and increase in operational temperatures. Although presently used diaphragms are robustly designed and operate safely, in some instances the diaphragm may not prevent an undesired change to the flow rate setpoint of the valve when exposed to high temperatures.
One particular type of undesired change to the flow rate setpoint following repeated pressure cycles results from an increase in the radial tension across the diaphragm. More particularly, as the flow control valve body temperature increases, the metallic housing holding the diaphragm in place is subjected to increased temperatures and thermally expands. This thermal expansion of the diaphragm housing increases the outer diameter bolt pattern that is securing the diaphragm. During this situation, the fabric comprising the diaphragm may not allow the diaphragm to stretch in response to the increased outer diameter. This increase in the outer diameter bolt pattern can result in an increase in the radial tension in the diaphragm, thereby introducing a force in the axial direction which is attempting to return the diaphragm to its natural center position. More particularly, the radial stretch is translated into an axial force. This translation of force is known as the radial spring rate in the diaphragm, where in this case with fabric, the spring rate is relatively high. The axial forces can upset the original, calibrated, zero delta-pressure balance and result in an undesired change to the flow rate setpoint of the valve when exposed to high temperatures that may compromise valve performance.
Hence, there is a need for a diaphragm that may be used in a flow control valve that is less prone to producing a high radial spring rate and/or is relatively inexpensive to make and/or reduces maintenance and repair costs associated with diaphragms. The present invention addresses one or more of these needs.